Low noise cable providing communication between electronic sensor components and patient monitor

ABSTRACT

A physiological measurement system can include a low noise patient cable that connects a monitor and a noninvasive optical sensor. The cable has a plurality of emitter wires configured to communicate a drive signal between the monitor and at least one emitter. The cable also has a plurality of detector wires configured to communicate a physiological signal between at least one detector responsive to the emitter and the monitor. The emitter and detector wires are orthogonally disposed so that crosstalk between the two functionally different wires is mitigated.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.13/536,881, filed Jun. 28, 2012, pending, which claims a prioritybenefit under 35 U.S.C. §119(e) from U.S. Provisional Patent ApplicationSer. No. 61/502,740, filed on Jun. 29, 2011, titled “Low Noise PatientCable” The '740 provisional application is incorporated by referenceherein in its entirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. Publication No. 2003/0212312,filed on Dec. 19, 2002, entitled “Low Noise Patient Cable,” which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure generally relates to patient monitoring devicesand more specifically, embodiments of the present disclosure relate tocables connecting a monitor and a sensor of the patient monitoringdevice.

2. Description of the Related Art

Physiological measurement systems using spectroscopic analysis are awidely accepted noninvasive procedure for measuring patientcharacteristics such as oxygen and glucose levels. Measuring thesecharacteristics is important for patient wellness because for instance,an insufficient supply of oxygen can result in brain damage and death ina matter of minutes. Thus, early detection of low blood oxygen level isof crucial importance in the medical field, especially in critical careand surgical applications. Patient monitors commercially available fromMasimo Corporation of Irvine Calif., USA, measure many physiologicalparameters including oxygen saturation, pulse rate, perfusion,carboxyhemoglobin, methemoglobin, total hemoglobin, glucose, overallwellness, respiration, combinations of the same and others.

As shown in FIGS. 1A and 1B, a physiological measurement system consistsof a monitor 101, a noninvasive optical sensor 115 applied to a patient,and a cable 111 connecting the sensor and the monitor. The system iscontrolled using input keys. The monitor 101 may be a portablestandalone device or may be incorporated as a module or built-in portionof a multiparameter patient monitoring system. The monitor displaysmeasurements of various physiological patient characteristics on adisplay 105, which may include an oxygen saturation level, a pulse rate,and an audible indication of each pulse via a speaker 107. In addition,the monitor 101 may display the patient's plethysmograph, which is avisual display of the patient's pulse contour and pulse rate, as well asa myriad of other measurements and calculated parameters.

To perform the above functions, the monitor 101 energizes one or moreemitters in the sensor 115 that irradiate tissue under observation, suchas, for example, a finger, toe, foot, hand, ear, forehead or the like.The radiation from the emitters is scattered and absorbed by the tissuesuch that some attenuated amount emerges and is detected through one ormore detectors located in the sensor 115. The detector(s) produces oneor more signal(s) indicative of the intensity of the detected attenuatedradiation and forward the signal(s) to the patient monitor 101 forprocessing. The sensor 115 that houses the emitters and the detectorscan be disposable, reusable, or partially reusable and disposable.Reusable sensor may include a clothespin-shaped housing that includes acontoured bed conforming generally to the shape of a finger. The emitterand detector signals are transmitted over the cable 111 connecting themonitor and the sensor.

Depending on the nature of cables and the signals that are transmittedthrough cables, cables can be affected by a phenomenon known ascrosstalk. Crosstalk occurs when energy from one signal interferes withanother signal. Such interference can cause significant distortion inthe transmission of information which can lead to incorrect measurementsin physiological monitoring applications. As the cable 111 oftencommunicates high voltage emitter driving signals and low voltagesensitive detector signals, the cable 111 may unfortunately causeunwanted interference on the sensitive detector signals used todetermine measurements of the physiological parameters.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a low noise tinsel cable arrangementparticularly suited for transmitting communications between devices. Inan embodiment, the cable is used to transmit electrical signals betweena physiological sensor and a physiological monitor.

In an embodiment, the cable has one or more emitter wires configured tocommunicate drive signals between a monitor and at least one emitter.The cable also has one or more detector wires configured to communicatea physiological signals between at least one detector and the monitor.The emitter wires transmit relatively high energy drive signals, whilethe detector wires transmit lower energy physiological signals. Due tothe effect of crosstalk, the high energy drive/emitter signals candistort the lower energy physiological/detector signals.

This is especially problematic because, unlike the known emitter drivesignals generated by the monitor, the lower energy detector signal is anunknown signal. The unknown detector signal carries the importantphysiological patient information, such as, for example, signalsresponsive to absorption signals from the detector. Often, suchabsorption signals are lower energy signals and thus, often are moreeasily distorted. Thus, reducing interference with the detector signalsimproves system accuracy and reliability.

Existing solutions to reduce crosstalk on the detector signals includeuse of different twist rates and heavy shielding in a cable. Differenttwist rates of wire pairs do not fully mitigate crosstalk because atcertain points in the cable, the electromagnetic forces of the signalsmay still interact to cause interference. While a heavy shield betweenthe wires could potentially reduce the majority of the crosstalk, thismakes the cable stiff and thick. A bulky, cumbersome cable may pull thesensor away from an ideal position on the patient or pull it offaltogether, leading to erroneous physiological patient information.Moreover, heavy shielding is also more susceptible to stress fracturesfrom flexing of the cable, leading to a short lifespan. Thus, at leastbecause of the foregoing, heavy shielding is at least somewhat of animpractical solution for communicating signals from a sensor to aspectroscopic analysis device.

The present disclosure describes mitigating crosstalk by twisting theemitter wires about the central axis of the cable in an opposingrotational direction relative to the detector wires. Opposing twistsadvantageously seeks to create an angle between the two functionallydifferent wires that approaches 90 degrees. At such an angle, crosstalkis reduced without requiring heavy shielding. One embodiment twists thedetector wires in one direction down the center of the cable. Thedetector wires are insulated with an inner shield. Then the emitterwires are twisted in another direction around the inner shield such thatthe angle between the emitter wires and the detector wires is about 90degrees. Put in other terms, the detector wires are twisted clockwiseand the emitter wires are twisted counterclockwise, or vice versa. Theemitter wires are insulated with an outer shield, and a jacket isdisposed over the outer shield to form the cable.

The disclosed opposing rotation of the wires mitigates crosstalk fromthe opposing rotation. This may be without or in addition to differenttwist rates or shielding. Opposing rotation in the cable structure mayprovide a more flexible cable, thereby not hindering sensor placement ofthe patient.

In an embodiment, tinsel wires are used to form the cable. Tinsel wiresare relatively thin and strong. Using tinsel wires allows the cable tobe lighter and more flexible than equivalent all metal wires. Whilethinner wire is advantageous in some respects, reducing the cablediameter also increases the resistance through the wires. In anembodiment, the tinsel wires may also transmit the high energy drivesignals. In such embodiments, the increasing resistance places somelimitations on how small the cable diameter can be. The presentdisclosure accomplishes satisfactory signal transmission whilesimultaneously reducing the cable diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a perspective view of a physiological measurementsystem utilizing a noninvasive optical sensor.

FIG. 1B illustrates a perspective view of a portable physiologicalmeasurement system utilizing a noninvasive optical sensor.

FIG. 2 illustrates a perspective view of an embodiment of an uncoatedtinsel cable.

FIG. 3 illustrates a perspective view of an embodiment of a coatedtinsel cable.

FIG. 4 illustrates a cross sectional view of an embodiment of a lownoise patient cable.

FIG. 5 illustrates a top-down view of an embodiment of the cable of FIG.4.

FIG. 6 illustrates a cross sectional view of an embodiment of a lownoise patient cable.

FIG. 7 illustrates a block diagram of a simplified embodiment of a kinktesting apparatus for a cable.

FIG. 8 illustrates the testing apparatus of FIG. 7 with the cable in astretched position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1A and 1B (described in more detail below), aphysiological measurement systems 100 includes a monitor 101, a cable111, and a sensor 115. The sensor 115 can be any type of physiologicalsensor. Illustrated in FIGS. 1A and 1B are embodiments of noninvasiveoptical sensors. In the case of noninvasive optical sensors, the monitor101 sends drive signals to one or more emitters in the sensor 115 viathe cable 111. The emitters irradiate tissue under observation. One ormore detectors in the sensor 115 detect the radiation leaving the tissueand send a signal back to the monitor via the cable responsive to theattenuation. This sequence produces more accurate results when thenoninvasive optical sensor 115 remains substantially fixed with respectto the tissue of the patient. In the embodiment where the sensor 115comprises a reusable sensor, the sensor 115 is often held in place byonly the spring action of a clothespin-shaped housing. When a cable isstiff or bulky, as a patient moves to, for example, repositionthemselves, the torque from the stiff or heavy cable may be more thanthe tension provided by the spring, thus even slightly shifting theoptical components with respect to the measurement site on the tissue. Ashifted or dislodged sensor could lead to erroneous physiologicalpatient information.

As discussed in the foregoing, a stiff or bulky cable may be the resultof utilizing heavy shielding to reduce damaging crosstalk. Crosstalkoccurs when the drive/emitter signals interfere with thephysiological/detector signals, potentially leading to erroneousphysiological patient information, similar to but for different reasonsa shifted or dislodged sensor. Thus, a low noise patient cable accordingto the present disclosure advantageously balances reduction of stiffnessand size against the competing goal of reducing crosstalk.

Various embodiments described herein disclose a cable that is relativelythin and flexible, yet is still able to mitigate crosstalk. Oneembodiment includes the emitter wires twisted around the detector wiressuch that the angle between the two functionally different wires iswithin a range that creates a measurable difference in crosstalk. In anembodiment, the angle is about 90 degrees. In other embodiment, theangle ranges to either side of about 90 degrees where the reduction incrosstalk is measurable and advantageous in order to accommodate otherdesign goals, such as, for example, flexibility, shielding, etc.

By controlling the angle between the differing cables, the presentlydisclosed low noise cable advantageously reduces harmful crosstalkbefore considering additional gains that can be accomplished usingdifferent twist rates or heavy shielding.

Additionally, embodiments of the present disclosure include tinsel wiresand Kevlar material. Such construction materials advantageously providea cable structure that is relatively thin and flexible, yet strong. Itis noteworthy that the Applicants recognize that use of increasinglysmaller diameter cable is not necessarily the natural progression ofinnovation in medical cabling like the smaller is better concepts fromsemiconductor fabrication. In contrast to semiconductor fabrication, inpatient cabling innovation, reducing the cable diameter most oftenincreases the resistance through the thinner wires. Thus, as a cablediameter shrinks, the spectroscopic analysis devices become inoperableas signals cannot be effectively or even operably transmitted due to theincrease cable properties such as resistance.

Embodiments of the low noise cable described herein balance the issuesof cable diameter, resistance, shielding, etc. to disclose a cable thatis thin and flexible, yet still able to effectively communicate thedesired signals. This thin and flexible cable structure that mitigatescrosstalk advantageously increases accuracy and reliability.

FIG. 2 illustrates a simplified perspective view of an embodiment of anuncoated tinsel cable 200. Tinsel cables as used herein include theirordinary broad meaning understood by an artisan and, from the disclosureherein, include a non-conductive fiber 201, such as, for example, aramidfiber, that is coated with a thin layer of twisted conductive material203. In an embodiment, the conductive material 203 is a silver copperalloy. The non-conductive fiber 201 provides strength and flexibility,while the conductive material 203 allows transmission of electricalsignals. The conductive layer 203 is made very thin such that flexes inthe cable 200 do not cause fatigue.

FIG. 3 illustrates a simplified perspective view of an embodiment of acoated tinsel cable 300. The coated cable 300 includes the same orsimilar materials as the uncoated tinsel cable 200, but includes aplastic outer coating 205. In an embodiment, the plastic outer coating205 includes fluorinated ethylene propylene (FEP). An artisan willrecognize from the disclosure herein that other constructions seeking toelevate associated advantages may also be used.

FIG. 4 illustrates a simplified embodiment of a cross sectional view ofeach end of a low noise cable 400 according to portions of the presentdisclosure. The cable 400 includes an outer non-conductive protectivejacket 401, an outer shield layer 403, an outer core 405, an innershield 407, an inner core 409 and fiber filler 411. The outernon-conductive protective jacket 401 is made of flexible insulation. Inan embodiment, the protective jacket 401 is UV resistant polyurethaneand has a diameter of about 4.0 mm. The outer shield layer 403 is madeof twisted uncoated tinsel cable. The outer core 405 is made of a singlelayer of twisted coated tinsel cable. The inner shield 407 is again madeof twisted uncoated tinsel cable. The inner core 409 is also again madeof twisted coated tinsel cable, but also includes fiber fill 411 toprovide some structure to the inner core and to provide tensile strengthto help prevent the cable from tearing apart. In an embodiment, thefiber fill is made of Kevlar to provide added strength. In anembodiment, the fiber fill is made of aramid fiber. In an embodiment, asillustrated in FIG. 4, the cable has six fiber fill strands 411.

In an embodiment, as illustrated in FIG. 4, there are fifteen outer corewires 405 and fifteen inner core wires 409. In other embodiments, moreor fewer wires could be used depending on the application of the cableand the number of transmission paths needed. The various wires in theinner and outer cores 405 and 409 can have different colors ofinsulation for easy identification.

In order to minimize crosstalk, the inner core 409 and the outer core405 are twisted in opposing rotational directions. FIG. 5 illustratesthe manner in which, in embodiments disclosed herein, wires in an innercore are twisted in an opposing fashion relative to wires in an outercore. FIG. 5 shows a simplified top-down view of a cable 500, whichincludes inner wires 502 in an inner core twisted about the central axisof the cable 500 in a helical fashion. The cable 500 also includes outerwires 504 in an outer core, which are also twisted about the centralaxis of the cable 500 in a helical fashion but in an opposing rotationaldirection from the inner wires 502. The angle θ shown in FIG. 5indicates the angle between the outer wires 504 and the inner wires 502.Interference and crosstalk between the outer wires 504 and the innerwires 502 are reduced as the angle θ approaches 90 degrees from eitherdirection.

For example, in one embodiment, the inner core is twisted clockwise andthe outer core is twisted counter clockwise. This arrangement causes theouter core cables to be at about an angle of greater than 90 degrees toinner core cables, assisting in reducing crosstalk. In an embodiment,the angle is between about 60 and about 120 degrees. In anotherembodiment, the angle is between about 60 and about 90 degrees, and in afurther embodiment, the angle is about 90 degrees. In still anotherembodiment, the angle is about 60 degrees.

In an embodiment, the inner core is used to transmit the relatively lowvoltage detector signals back to the monitor and the outer core is usedto transmit the relatively high voltage emitter drive signals. In anembodiment, the emitter wires are the inner core wires and the detectorwires are the outer core wires.

FIG. 6 illustrates another embodiment of a low noise sensor cable. Inthis embodiment, tinsel cables are used in conjunction with standardwires, such as copper wires. In the outer core 605, there are four setsof three tinsel wires 635 and four sets of two standard wires 637 thatcan be any standard conducting wire such as copper. The inner core 609includes a set of triple twisted tinsel wires 641, four sets of twistedpair tinsel wires 639 and three standard detector wires 643. As in theembodiment of FIG. 4, the inner core 609 of the FIG. 6 embodimentincludes a fiber fill strand 411 to enhance the structure and tensilestrength of the cable. An inner shield layer 607 separates the innercore wires from the outer core wires. An outer shield layer 603surrounds the outer core 605. A jacket 601 is disposed over the outershield to form the cable.

Embodiments described herein show enhanced resilience to mechanicalstresses, such as kink resistance. Cables described herein andillustrated in FIG. 4 were tested to determine their resistance toelectrical failure due to mechanical breakdown of the internalconductors and/or shielding after the cable is subjected to repeatedattempted kinking. FIG. 7 illustrates the test setup. The setup includesa cable 700 secured into, for example, two mounting blocks 710, 712. Asection of, for example, at least about twelve (12) inches of cable 700is used for testing. Before the cable 700 is secured to the mountingblocks 710, 712, two positions on the cable 700 approximately seven toeight inches apart are marked, and the cable 700 is grasped at thosemarks and twisted approximately 720 degrees. This twisting causes thecable to form a loop 740 as shown in FIG. 7, and the cable 700 is thensecured to the mounting blocks 710, 712 at the marked positions.

The mounting blocks 710, 712 are attached to a track 718. The firstmounting block 710 is fixed to the track 718, and the second mountingblock 712 is slidably attached to the track 718. The second mountingblock is also attached to a guide block 722, which is in turn driven bya pneumatic cylinder 724. The pneumatic cylinder 724 receives an airsupply of approximately about 100 psi, which is regulated down to about50 psi. This arrangement allows a tensile force of approximately 5-7lbf. to be applied to the cable 700. When the pneumatic cylinder 724pushes the guide block 722 and then pulls it back to the startingposition, this constitutes one cycle of the test.

FIG. 7 shows the testing apparatus when the pneumatic cylinder 724 is atits starting position. Because no tensile force is being applied to thecable 700, the loop 740 is present. FIG. 8 shows the same testingapparatus when the pneumatic cylinder 724 is pushing on the guide block722, therefore applying a tensile force to the cable 700. The effect ofthis tensile force is to attempt to produce a kink 742 in the cable 700.

The two ends 702, 704 of the cable 700 are electrically connected to abreak detect circuit test box 730. The box 730 senses when a significantchange of resistance occurs in the cable 700, and when this occurs, thebox 730 sends a signal to the pneumatic cylinder 724 to stop thetesting. Thus, this test repeatedly subjects the cable 700 to kinkinguntil an electrical failure occurs. The number of cycles the cable 700can withstand before electrical failure is an indicator of itsresilience to mechanical stresses.

Twelve cable samples were subjected to this test. The results of thetesting are shown below:

Sample Cycles to Failure 1 13,820 2 6,831 3 12,053 4 9,781 5 8,493 66,808 7 9,232 8 23,781 9 18,842 10 15,205 11 15,248 12 17,395

As the table shows, the smallest number of cycles producing anelectrical failure for the twelve samples tested was 6,808 cycles andthe largest was number of cycles was 23,781. The mean cycles-to-failurewas 13,124 and the median was 12,937. These results demonstrate that thecable described herein exhibit enhanced resilience to mechanical stress.Cables described herein are capable of withstanding more than 1,500kinks with a high degree of reliability. Reliability can be measuredusing a Weibull Distribution Model. Applying that model with a shapeparameter of Beta=1.7, in order for the cable to reliably withstand1,500 kinks, none of the twelve samples tested should have a failureafter 6,583 kink cycles. Because the smallest number of cycles producingan electrical failure for the twelve samples tested was 6,808 cycles,the cable tested is capable of withstanding more than 1,500 kinks with ahigh degree of reliability. The cables described herein are capable ofwithstanding, on average, more than 5,000 kinks. More particularly, thecables described herein are capable of withstanding, on average, morethan 10,000 kinks. Still more particularly, the cables described hereinare capable of withstanding, on average, more than 12,500 kinks. In anembodiment, the cables described herein are capable of withstanding inthe range or 0 to 23,000 kinks.

FIGS. 1A and 1B illustrate perspective views of physiologicalmeasurement systems utilizing a noninvasive optical sensor. Referringspecifically to FIG. 1A, the physiological measurement system 100 has aportable monitor 101 and docking station 103 that houses the portablemonitor 101. The portable monitor 101 has a display 105 to showphysiological measurement data. The measurement data provides a readoutof blood analytes, such as oxygen, carbon monoxide, methemoglobin, totalhemoglobin, glucose, proteins, glucose, lipids, a percentage thereof(e.g., saturation), or other physiologically relevant patientcharacteristics. The portable monitor also has a speaker 107 to provideaudible monitoring of physiological measurements, including, forexample, the pulse rate. Utilizing control buttons, a user can operatethe physiological measurement system and select between differentavailable measurement data or other functionality for the user tomanipulate, such as alarm settings, emitter settings, detector setting,and the like.

A cable 111 docks into a monitor sensor port 113 and connects to anoninvasive optical sensor 115 that is fitted on a patient utilizing aclothespin-shaped enclosure with a contoured bed conforming generally tothe shape of a finger. The cable 111 can be of various lengths to allowfor separation between the portable monitor 101 and sensor 115. Thenoninvasive optical sensor 115 has a set of emitters and detectors. Theemitters serve as the source of optical radiation to irradiate patienttissue. The portable monitor 101 sends a drive signal to the emittersvia the monitor sensor port 113 and through the cable 111. The emittersproduce optical radiation using one or more sources of opticalradiation, such as LEDs, laser diodes, incandescent bulbs withappropriate frequency-selective filters, combination of the same, or thelike. The radiation from the emitters is scattered and absorbed by thetissue such that some attenuated amount emerges and is detected by oneor more detectors. The detectors produce a signal indicative of theintensity of the detected attenuated radiation and forward the signalvia the cable through the monitor sensor port to the portable monitorfor processing.

FIG. 1B illustrates a perspective view of another portable physiologicalmeasurement system 150 utilizing a noninvasive optical sensor 151. Thesystem of FIG. 1B is similar to that of FIG. 1A described above exceptthat the monitor 155 is a portable standalone device instead of beingincorporated as a module or built-in portion of the physiologicalmeasurement system. Moreover, the physiological measurement system 150in FIG. 1B includes advanced functionality involving additional emitterand detectors in the sensor 151. This allows the patient physiologicalmeasurement system 150 to determine more difficult to detect parameterssuch as, for example, glucose and total hemoglobin. Moreover, the cable153 is required to transmit more sensitive data that is easily corruptedby cross talk and other interference. As a result, the cabling describedin the present disclosure is particularly suited to use in the patientmonitor of FIG. 1B. The monitor 155 has a display 157 to showphysiological measurement data and control buttons 159 that allow a userto operate the physiological measurement system 150 and select betweendifferent available measurement data or other functionality.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors. In addition, some or all code from a single module may bestored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

Although the foregoing invention has been described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art from the disclosure herein. For example,additional or alternative materials may be used to enhance the low noisecable for the known properties of the additional or alternativematerials without detracting from the novelty of the present disclosure.Moreover, different or additional testing apparatuses than those ofFIGS. 7 and 8 may provide useful insight into the flexibility and/ornoise reduction of the present disclosure. Additionally, othercombinations, omissions, substitutions and modifications will beapparent to the skilled artisan in view of the disclosure herein.Accordingly, the present disclosure is not intended to be limited by thereaction of the preferred embodiments, but is to be defined by referenceto the appended claims.

Additionally, all publications, patents, and patent applicationsmentioned in this specification are herein incorporated by reference tothe same extent as if each individual publication, patent, or patentapplication was specifically and individually indicated to beincorporated by reference.

1. A low noise patient cable comprising: a plurality of detector wiresconfigured to communicate a physiological signal between a detector,which is responsive to energy received from an emitter, and a monitor; ashield disposed over the plurality of detector wires; a plurality ofemitter wires configured to communicate a drive signal between themonitor and at least one emitter, wherein the plurality of emitter wiresare twisted in an opposing rotational direction relative to theplurality of detector wires; and a jacket comprising the plurality ofdetector wires, the shield, and the plurality of emitter wires, whereina thickness of the shield is less than or equal to 4 mm.
 2. The lownoise patient cable of claim 1, wherein an angle between the pluralityof emitter wires and the plurality of detector wires is between about 60degrees and about 90 degrees.
 3. The low noise patient cable of claim 2,wherein the plurality of detector wires are tinsel wires.
 4. The lownoise patient cable of claim 2, further comprising a plurality fillerwire.
 5. The low noise patient cable of claim 4, wherein the pluralityfiller wires comprise at least one of the following: kevlar wires andaramid wires.
 6. The low noise patient cable of claim 2, furthercomprising a second shield disposed over the plurality of emitter wires.7. (canceled)
 8. A method of making a cable, the method comprising:twisting in a first direction a plurality of inner core wires; using ashield over the plurality of inner core wires that does not limitflexibility of the cable; twisting in a second direction a plurality ofouter core wires around the shield, the second direction being oppositethe first direction; and disposing a jacket around the plurality ofouter core wires.
 9. The method of claim 8, further comprising twistinga plurality of filler wires with the plurality of inner core wires. 10.The method of claim 8, further comprising disposing a second shieldaround the plurality of outer core wires.
 11. The method of claim 8,further comprising twisting a plurality of filler wires with theplurality of inner core wires.
 12. The method of claim 11, wherein thefiller wires are aramid.
 13. The method of claim 11, wherein the fillerwires are Kevlar.
 14. The method of claim 8, wherein the inner and outercore wires are tinsel wires.
 15. The method of claim 14, wherein thetinsel wires are made from a silver copper alloy.
 16. A low noisepatient cable comprising: a plurality of inner core wires twisted abouta central axis of the cable in a first direction, the plurality of innercore wires being configured to communicate a first electrical signal; ashield disposed over the plurality of inner core wires, the shieldhaving a thickness that maintains flexibility of the plurality of innercore wires and the outer core wires, wherein the thickness is less thanor equal to a diameter of a jacket; a plurality of outer core wirestwisted about the central axis in a second direction, the seconddirection being opposite the first direction, wherein the plurality ofouter core wires are configured to communicate a second electricalsignal, wherein the low noise patient cable does not electrically failafter being kinked more than 1,000 times.
 17. The low noise patientcable of claim 16, wherein the plurality of inner core wires are tinselwires.
 18. The low noise patient cable of claim 17, wherein the tinselwires are a silver copper alloy.
 19. The low noise patient cable ofclaim 16, further comprising a plurality filler wires twisted with theinner core wires.
 20. The low noise patient cable of claim 16, furthercomprising a second shield disposed over the plurality of outer corewires. 21.-27. (canceled)